1. Field of the Invention
This invention relates to an electric power distribution unit constituting an electric power distribution circuit extending from a vehicle-mounted electric power source in a vehicle such as an automobile or the like, and to an electric connection box having the unit.
2. Description of Related Art
Heretofore, an electric connection box, in which an electric power distribution circuit is formed by stacking a plurality of bus bar boards, and in which fuses and relay switches are incorporated for distributing electric power from a common vehicle-mounted electric power source to various electronic unit, has been generally known.
Further, in order to reduce a size of such electric connection box and to implement switching control, an electric connection box has been developed recently in which semiconductor switching devices, such as field effect transistors (FETs) or the like are interposed between input and output terminals in lieu of the relay switches.
However, since these semiconductor switching devices have a relatively great calorific power, it is necessary to efficiently remove heat from the devices.
An electric connection box is disclosed in, for example, Japanese Laid-Open Patent Application No. 2001-319708 as one way of solving the problem. The electric connection box includes an electric power distribution section having an input terminal to be connected to an electric power source, output terminals, semiconductor switching devices interposed between the input and output terminals, and a bus bar circuit section, having a metallic bus for forming a circuit and an insulation plate stacked on the bus bar, for connecting the respective output terminals of the electric power distribution section to vehicle-mounted loads. The electric power distribution section and bus bar circuit section are assembled in a common case with a part of bus bars in the bus bar circuit section being connected to the respective output terminals of the electric power distribution section.
In more detail, in the above-described electric connection box, the input terminal bus bar and the plurality of output terminal bus bars are disposed at a rear side of the heat radiation member, semiconductor switching devices are interposed between the input and output terminal bus bars for switching an ON-OFF energization of the input and output terminal bus bars, and heat generated from the semiconductor switching devices is radiated through the heat radiation member to the outside.
According to such an electric connection box, since the electric power distribution section including the semiconductor switching devices and heat radiation member is provided independently of the bus bar board as an electric power distribution unit, it is possible to efficiently cool the respective semiconductor switching devices at a single position concentrically.
Although switching means for switching an ON-OFF energization of the input and output terminals consist of only the semiconductor switching devices in the above-mentioned disclosure, there are occasions where the semiconductor switching devices alone cannot carry out the ON-OFF energization in a special specification. In this case, it is necessary to use conventional relay switches and semiconductor switching devices together.